The objective of this Phase II proposal is to develop and test a breath sample system that will increase the breath alcohol test accuracy from - 50% to plus or minus 6% when attached to commercially available breath test devices. The sample system will use the Isothermal Rebreathing technology developed by Meridian to eliminate the physiological errors associated with current systems. Meridian confirmed in its Phase I work that the errors could be reduced to this extent while retaining the same ease of use found in current commercial units. During the proposed two year Phase II, a preproduction prototype sample system will be designed, fabricated, laboratory tested on humans, field tested by law enforcement personnel, and submitted to the federal Department of Transportation for approval.